Steering controllers are well known for controlling fluid flow to operate the power steering systems of off the road vehicles such as trucks, farm tractors, farm combines, and end loaders, etc. Such controllers are typically designed to meter flow from a source (e.g., the power steering pump) and direct the metered flow to power the vehicle steering motor.
In steering controllers known as integral controllers a control valve section and a metering section are disposed within a housing which is usually formed by one or more cast iron housing members. In the absence of steering effort, the control valve section is in a neutral condition in which no flow is directed to the steering motor. In response to operation of an input shaft connected with the vehicle steering wheel, the control valve section is moved away from the neutral condition into an operating condition in which the valve section directs flow from the source to the metering section, and directs metered flow from the metering section to the steering motor. When operation of the steering wheel ceases, the control valve section is returned to the neutral condition.
U.S. Pat. No. 3,895,888 discloses one such controller. The controller includes a metering mechanism formed by the intermeshing teeth of a pair of gerotor gear members having relative orbital and rotational movement. An input shaft is fixedly coupled with one gerotor gear member to rotate one of the gerotor gear members therewith. The other gerotor gear member is coupled with a rotatable control valve element and, in response to rotation of the one gerotor gear member, effects rotation of the control valve element by a limited extent from a neutral condition to place the controller in an operating condition. At FIGS. 14-16 the patent discloses a controller in which the control valve includes a rotatable plate valve and provides a very compact structure.
Some steering controllers have also been designed so as to be capable of not only metering needed flow to the steering motor, but also directing excess flow to an auxiliary motor associated with equipment such as backhoes, lifting devices, etc. carried by the vehicle. U.S. Pat. Nos. 3,834,278 and 4,050,474 disclose such types of controllers. In U.S. Pat. No. 3,834,278 an axially movable valve element controls flow from a source in response to rotation of an input shaft connected with the vehicle steering wheel. When the controller is in a neutral condition, all flow from the source is directed to the auxiliary motor. When the controller is placed in an operating condition, needed flow to the steering motor is metered and directed to the steering motor, and excess flow is directed to the auxiliary motor. In U.S. Pat. No. 4,050,474 a control valve comprises a pair or rotatable valve members coupled together by a lost motion connection. One valve element is fixed with the input shaft and the other valve element is connected with one of a pair of gerotor gear elements forming the metering section.
The controller of each of the foregoing patents includes a fairly large, complex cast housing member. In the controllers of U.S. Pat. Nos. 3,834,278 and 4,050,474 the cast housing members enclose the valve section and also include parts of the flow control passages. In U.S. Pat. No. 3,895,888, a cast housing member encloses the metering section and the rotatable plate valve member, and also forms an opening shaped to receive the bearings and seals which support and seal the input shaft. To form such cast housing members properly usually requires a number of precise machining steps. Also, the cast members are usually bulky, and, being cast of iron, constitute a significant portion of the overall weight of the controller.
The controller disclosed in each of the foregoing patents also includes a spring centering mechanism which biases the control valve toward a neutral condition. Rotation of the input shaft actuates the valve element against the bias of the spring centering mechanism. In U.S. Pat. No. 3,895,888 (FIGS. 14-16) the spring centering mechanism includes a spherically shaped detent which is spring biased in a radial direction into a V-shaped groove in the rotatable plate valve member. In U.S. Pat. No. 3,834,278 the spring centering mechanism comprises a torsion rod disposed on a bore within the axially movable valve member. The torsion rod is twisted or wound by movement of the valve member away from neutral, and unwinds to urge the valve member to the neutral condition when steering effort ceases. In U.S. Pat. No. 4,050,474 the spring centering mechanism comprises a series of leaf springs compressed against the housing and against the relatively rotatable valve members.
The controller of U.S. Pat. No. 3,834,278 also has pressure dams for blocking leakage of metered fluid to a low pressure return port when the controller is in an operating condition. Pressure dam grooves are disposed between grooves at metered fluid pressure and at return pressure. In neutral, inlet fluid pressure, which is close to metered fluid pressure, is communicated with the pressure dam grooves. When the controller is in an operating condition only one pressure dam groove is needed to block leakage of metered fluid to return. The other pressure dam groove forms part of a flow passage directing flow from the motor to a reservoir. In such controllers a check valve or a specially designed orifice is usually used to minimize flow from the pump through whichever pressure dam groove is in the latter condition.
In U.S. patent application Ser. No. 944,703, a controller is disclosed in which pressure dams are formed in a different manner. Specifically, in neutral there is communication between the pump and the reservoir through the pressure dam grooves. Check valves are used to minimize flow through the pressure dam grooves in this condition. Pressure dams are created by relative movement of a pair of valve members to an operating condition in which they block flow through the pressure dam grooves.
The controller of U.S. Pat. No. 3,834,278 also shows a typical dynamic seal arrangement for minimizing leakage of high pressure fluid about the input shaft. A specially formed bore in the housing encircles the input shaft, and an arrangement of elements forming a dynamic seal are disposed between the bore in the housing and the rotatable input shaft.